Without co2 supplementation, a good range is 600 to 800 ppfd. Beyond 800ppfd there is greatly diminishing returns on more light intensity.
I use the free lux light meter app on my android phone
Install:
https://play.google.com/store/apps/details?id=com.doggoapps.luxlight
It uses the light sensor on your phone, the same one that auto adjusts screen brightness or makes the camera flash when you use the auto flash setting.
If you use a lux to ppfd converter like this one
Online calculator to convert illuminance (lux) to PPFD (micromoles per second per meter squared).
www.waveformlighting.com
Online calculator to convert PPFD (micromoles per second per meter squared) to illuminance (lux).
www.waveformlighting.com
You will see that a range of 38000lux to 49000lux on a 3500k 80cri LED puts you in the 600ppfd to 800ppfd range.
Of course, this is not as good as having a proper par meter, but it's free. I find it very useful.
The output values on the app depend on the phones hardware, and how it interprets the signals from the sensors. I first baseline it under a known good light, so I know what range is good. Mine seems to measure acceptably correct lux values on my phone.